30 Cutler, Parthenogenesis in Animals 



substances, which alter the power of v the protoplasm to absorb 

 water. This view has, however, been partially given un» by the. 

 author in favour of a later one, in which} 'it is suggested that 

 the ions act by their electric charges causing modifications of 

 those of the colloids. 



Loeb definitely established that oxidisation is increased by 

 membrane formation, and this oxidation, if allowed to continue, 

 prevents development from proceeding further than a few cell 

 cleavages. The action of the hypertonic solution, which enables 

 development to continue to late stages, is to inhibit or alter the 

 internal oxidations of the egg. Further, the solution must be 

 alkaline, if neutral the egg 'breaks up into vesicles ; also the 

 action of the solution will only take place in the presence of free 

 oxygen. In what way then is the development influenced? 

 Here again Loeb's explanation is chemical. The solution causes 

 the formation of a substance or substances which orientate the 

 development into the right direction, or control the first phase, 

 that is, the membrane formation phase. This is brought about 

 by the synthesis from the protoplasm^ of specific nuclein sub- 

 stances of the nucleus, and this synthesis is again the result of 

 an oxidation which is not of the Same nature as the first one. It 

 is necessary to note that this second oxidation is not the direct 

 result of the hypertonic solution, but is a consequence of dehy- 

 dration. Dehydration produces changes in the chemical equili- 

 brium of the protoplasm, resulting in the dissociation of electro- 

 lytes. Loeb thus concludes that the sperm in fertilisation brings 

 into the egg two substances : — 



(i) A catalyser which causes membrane formation. 



(2) A corrective substance which modifies the action of the 

 first producing normal development. 



The foregoing theories are highly ingenious, but are perhaps 

 too speculative in character to be taken as explaining the whole 

 process of fertilisation. Also the author is so inculcated with 

 the chemical aspects of the problem that he is in danger of 

 overlooking the probability that many of the phenomena may 

 have physical explanations. 



Further, as will be seen later, there are many eggs of various 

 species of animals which do nojt require to be treated by the 

 above methods; for instance, there is no need to use hypertonic 

 sea-water in order to obtain parthenogenesis in the eggs of 

 Polynoe, Lottia or Acmsea. These if acted upon by catalytic 

 substances and then transferred to alkaline solutions, hyper- 

 tonic or not, will readily develop. 



